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- 2. 2 1. SOURCE GROUNDED– EQUIPMENT UNGROUNDED EARTHING IN LV & MV SYSTEMS 2. SOURCE GROUNDED – EQUIPMENT GROUNDED 3. SOURCES GROUNDED – EQUIPMENT GROUNDED – WITH BONDING 4. LOW VOLTAGE (415V) 5. MV ( RESISTANCE GROUNDED SYSTEM ) 6. MV ( UNGROUNDED SYSTEM ) 7. ‘CLEAN’ EARTH 8. UPS SYSTEM EARTHING
- 3. 3 REFERENCES • IEEE Std– 80 : GUIDE FOR SAFETY IN AC SUBSTATION GROUNDING • IEEE Std – 1100 : GUIDE FOR POWERING AND GROUNDING ELECTONIC EQUIPMENT • IS – 3043 : CODE OF PRACTICE FOR EARTHING • EARTHING PRINCIPLES AND PRACTICES : R W RYDER • ELECTRICAL EARTHING AND ACCIDENT PREVENTION : EDITED BY M G SAY
- 4. 4 EARTHING IN LV& MV SYSTEMS 1. SOURCE GROUNDED – EQUIPMENT UNGROUNDED • AB – SOURCE OF SUPPLY; C – EQUIPMENT • B IS EARTHED TROUGH EARTH ELECTRODE 'E' • FOR EASY CONCEPTUALIZATION, 1 NETWORK SHOWN A V B E1 C H
- 5. 5 • UNDER NORMALCONDITIONS, R VERY HIGH. EVEN IF A PERSON TOUCHES THE BODY, NO CURRENT FLOWS THROUGH HIM • INSULATION FAILURE OF EQUIPMENT R = 0 • CURRENT THROUGH PERSON V 240 H = ------------ = ------------ 120 mA RH + RE1 2000 + 1 • THIS CURRENT IS SMALL AND NOT SUFFICIENT TO BLOW THE FUSE • BUT EVEN THIS SMALL CURRENT CAN BE DANGEROUS TO A PERSON ( IEEE STD - 116 mA FOR 1 Sec ) A RC R X RH C B RE1 V
- 6. 6 2. SOURCE GROUNDED– EQUIPMENT GROUNDED • B & C ARE EARTHED THROUGH EARTH ELECTRODES 'E1' & 'E2' • INSULATION FAILURE OF EQUIPMENT R = 0 • REQ = RE2 RH = 1 2000 = 1 C F RC R X RE1 RE2 RH A B V
- 7. 7 • FAULT CURRENT •F IS SIGNIFICANT BUT NOT VERY HIGH. FUSE MAY OR MAY NOT BLOW • H - CURRENT THROUGH PERSON LOW BUT NOT INSIGNIFICANT V F = ------------ REQ + RE1 240 = ------------ 120 A 1 + 1 < 120 mA > 1 H = ----------- x 120 60 mA 1 + 2000 < 120 mA > C F RC R X RE1 RE2 RH A B V
- 8. 8 • BONDING CONDUCTOR– SHOWN IN RED • PHYSICAL CONNECTION BETWEEN EQUIPMENT CASING AND SOURCE • ALSO CALLED EARTH CONTINUITY CONDUCTOR • BONDING CONDUCTOR RESISTANCE : RB VERY SMALL 3. SOURCE GROUNDED – EQUIPMENT GROUNDED – WITH BONDING • FIG_EA_20
- 9. 9 240 F = ---------= 24 kA 0.01 • F IS VERY HIGH. FUSE WILL BLOW INSTANTANEOUSLY. • HUMAN SAFETY INHERENTLY ACHIEVED • CONCLUSION DO NOT DEPEND ON 'MOTHER EARTH' FOR RETURN OF FAULT CURRENT. DEPEND ON PHYSICAL EARTH CONTINUITY CONDUCTOR (BONDING) THAT RUNS FROM EQUIPMENT TO SOURCE. • EVEN ASSUMING RB = 0.01 , FAULT CURRENT • FIG_EA_20 IF FAULT CURRENT IS NOT DISCHARGED TO EARTH, STEP & TOUCH POTENTIALS ARE IRRELEVANT.
- 10. 10 1- F SUPPLYTO EQUIPMENT A A RC R V X RE1 RB RE2 RH E2 EQUIPMENT GROUNDED WITH BONDING E1 B H B C C V FIG_EA_20 SOURCE GROUNDED
- 11. 11 1- F SUPPLYTO EQUIPMENT A A RC R V X RE1 RB RE2 RH E2 EQUIPMENT GROUNDED WITH BONDING E1 B H B C C V FIG_EA_20 SOURCE GROUNDED
- 12. 12 4. LOW VOLTAGE(415V) • GENERALLY SOLIDLY GROUNDED • IE RULES • IF FOR ANY REASON, IF LV SYSTEM IS NOT SOLIDLY GROUNDED, SPECIAL PERMISSION FROM ELECTRICAL INSPECTOR REQUIRED • MYTH : EARTH IS GOOD EQUIPMENT GROUNDING CONDUCTOR • REALITY : EARTH IS THE MOST UNRELIABLE EQUIPMENT GROUNDING CONDUCTOR
- 13. 13 • BEST EARTHELECTRODE RESISTANCE 1 • ON 415 V SYSTEM, IF ONLY EARTH IS USED FOR RETURN OF FAULT CURRENT, MAX (415/3) / 1 MAX 240 AMPS • IF FAULT CURRENT IS LIMITED TO 240 A, NEITHER O/C RELAY NOR FUSE WILL EVER OPERATE ! • FIG_EA_1 EARTH : UNRELIABLE EARTHING CONDUCTOR
- 14. 14 FIG_EA_1 ACCIDENTAL CONTACT SWITCHGEAR N R E= 1 E VTOUCH SOLIDLY GROUNDED NEUTRAL
- 15. 15 • EARTH SHALLNOT BE TREATED AS SOLE EQUIPMENT GROUNDING CONDUCTOR FOR FAULT CURRENT RETURN PATH • MAKE AS MANY SUPPLEMENTARY CONNECTION TO EARTH FROM EQUIPMENT AS YOU WISH • BUT MAKE SURE THAT ALL EQUIPMENT ARE CONNECTED TO GROUNDING GRID (EARTH CONTINUITY) CONDUCTOR WHICH SHALL BE CONNECTED TO SOURCE NEUTRAL • CONCLUSIONS
- 16. 16 • MAJORITY OFFAULT CURRENTS SHALL BE CARRIED BY GROUNDING GRID CONDUCTOR AND VERY LITTLE BY 'MOTHER' EARTH • IF EARTH CURRENT IS LESS, TOUCH POTENTIAL IS ALSO LESS • FIG_EA_26 • IF NOT DONE LEADS TO GROUND FAULT RELAYING PROBLEMS • EARTH CONDUCTOR MUST RUN ALL OVER THE PLANT AND MUST CARRY RETURN CURRENT BACK TO SOURCE NEUTRAL LOW VOLTAGE (415V) • CORRECT METHOD FIG_EA_99A • WRONG METHOD FIG_EA_99B
- 17. 17 FIG_EA_26 SOLIDLY GROUNDED SYSTEM 6.6kV 415V BKR R Y B N E
- 18. 18 EARTHING IN LVSYSTEM CORRECT METHOD M E MCC E PCC R Y B N 6.6KV E 40 x 6 FIG_EAR_99A 415V
- 19. 19 EARTHING IN LVSYSTEM WRONG METHOD M E MCC E PCC R Y B N 6.6KV E 40 x 6 FIG_EAR_99B E 415V
- 20. 20 • UNSAFE EARTHING •NO EARTH CONTINUITY CONDUCTOR • SAFE EARTHING • WITH EARTH CONTINUITY CONDUCTOR
- 21. 21 • EVEN HERETHE EARTH CONDUCTOR MUST RUN ALL OVER THE PLANT AND MUST CARRY RETURN CURRENT BACK TO NGR 5. MV ( RESISTANCE GROUNDED SYSTEM ) • FIG_EA_27 ANIMATION • DO NOT EARTH NGR BODY !
- 22. 22 FIG_EA_27 RESISTANCE GROUNDED SYSTEM 16kV 6.6 kV BKR R Y B NGR E
- 23. 23 CAUTION : DONOT EARTH NGR CUBICLE ! FROM TRANSFORMER OR GENERATOR NEUTRAL RESISTOR STACKS TO EARTH GRID EARTH PIT NGR SUPPORT FRAME EARTH PIT INSULATOR SHEET STEEL ENCLOSURE SOIL LEVEL TO EARTH GRID BUSHING
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- 25. 25 6. MV (UNGROUNDED SYSTEM ) • FIG_EA_28 • EVEN FOR UNGROUNDED SYSTEM EARTH CONTINUITY CONDUCTOR RECOMMENDED ! • FIG_EA_47
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- 27. 27 FIG_EA_47 EARTHING CONDUCTOR INUNGROUNDED SYSTEM M M
- 28. 28 7. ‘CLEAN’ EARTH ❖ELECTRONIC EQUIPMENT EARTHING • FIG_EA_51 - CORRECT METHOD • FIG_EA_52 - WRONG METHOD • FIG_EA_53 - MONITORING • NEUTRAL CURRENT HIGH • CURRENT THROUGH ISOLATED GROUND HIGH
- 29. 29 ‘CLEAN’ EARTH • TWOCARDINAL PRINCIPLES • NEUTRAL CONDUCTOR AND GROUND CONDUCTOR CONNECTED ONLY AT THE SERVICE ENTRANCE. FROM THIS POINT ON, NEUTRAL AND GROUND CONDUCTORS SHOULD NOT BE BONDED TOGETHER. i.e. NEUTRAL AND GROUND CONDUCTORS SHOULD NEVER TOUCH EACH OTHER AFTER LEAVING SERVICE ENTRANCE PANEL BOARD. • UNBALANCED LOAD CURRENTS SHALL RETURN ONLY THROUGH THE NEUTRAL BACK TO THE SERVICE ENTRANCE. GROUND SHALL CARRY ONLY FAULT CURRENT AND NOT UNBALANCED LOAD CURRENTS.
- 30. 30 • MYTH ELECTRONIC EQUIPMENTREQUIRE A ‘CLEAN, DEDICATED AND ISOLATED GROUND’ AND SHOULD BE ISOLATED FROM DIRTY ‘POWER EARTH’. THIS IS A FAIRY TALE AND NOT AS PER CODES. ‘CLEAN’ EARTH
- 31. 31 N N ELECTRONIC EQUIPMENTEARTHING : CORRECT METHOD SOURCE PANEL RECEPTACLE LOAD N N N IG IG G G G FIG_EA_51
- 32. 32 ELECTRONIC EQUIPMENT EARTHING: WRONG METHOD CLEAN EARTH? N N SOURCE PANEL RECEPTACLE LOAD N N N IG IG G G G FIG_EA_52 POWER EARTH
- 33. 33 N N ELECTRONIC EQUIPMENTEARTHING- MONITORING SOURCE PANEL RECEPTACLE LOAD N N N IG IG G G G FIG_EA_53
- 34. 34 FIG_EA_26 SOLIDLY GROUNDED SYSTEM 6.6kV 415V BKR R Y B N E
- 35. 35 EARTHING IN LVSYSTEM CORRECT METHOD M E MCC E PCC R Y B N 6.6KV E 40 x 6 FIG_EAR_99A 415V
- 36. 36 UPS SYSTEM EARTHING NEUTRALAND GROUND BOND AT SERVICE ENTRANCE
- 37. 37 UPS SYSTEM EARTHING UPS- SEPARATELY DERVIED SOURCE
- 38. 38 UPS SYSTEM EARTHING DISTRIBUTIONBOARD - SEPARATELY DERIVED SOURCE
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